/*-------------------------------------------------------------------------
 *
 * nodeSeqscan.c--
 *    Support routines for sequential scans of relations.
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    $Header: /usr/local/cvsroot/postgres95/src/backend/executor/nodeSeqscan.c,v 1.3 1996/11/08 05:56:16 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
/*
 * INTERFACE ROUTINES
 *   	ExecSeqScan		sequentially scans a relation.
 *    	ExecSeqNext 		retrieve next tuple in sequential order.
 *   	ExecInitSeqScan 	creates and initializes a seqscan node.
 *   	ExecEndSeqScan		releases any storage allocated.
 *   	ExecSeqReScan		rescans the relation
 *   	ExecMarkPos		marks scan position
 *   	ExecRestrPos		restores scan position
 *
 */
#include "postgres.h"

#include "executor/executor.h"
#include "executor/execdebug.h"
#include "executor/nodeSeqscan.h"
#include "access/heapam.h"
#include "parser/parsetree.h"

/* ----------------------------------------------------------------
 *   			Scan Support
 * ----------------------------------------------------------------
 */
/* ----------------------------------------------------------------
 *	SeqNext
 *
 *	This is a workhorse for ExecSeqScan
 * ----------------------------------------------------------------
 */
TupleTableSlot *
SeqNext(SeqScan *node)
{
    HeapTuple	 	tuple;
    HeapScanDesc  	scandesc;
    CommonScanState 	*scanstate;
    EState	 	*estate;
    ScanDirection	direction;
    TupleTableSlot	*slot;
    Buffer		buffer;

    /* ----------------
     *	get information from the estate and scan state
     * ----------------
     */
    estate =        node->plan.state;
    scanstate =     node->scanstate;
    scandesc =      scanstate->css_currentScanDesc;
    direction =     estate->es_direction;

    /* ----------------
     *	get the next tuple from the access methods
     * ----------------
     */
    tuple = heap_getnext(scandesc, 		   /* scan desc */
			 ScanDirectionIsBackward(direction), /*backward flag*/
			 &buffer); 	           /* return: buffer */

    /* ----------------
     *	save the tuple and the buffer returned to us by the access methods
     *  in our scan tuple slot and return the slot.  Note: we pass 'false'
     *  because tuples returned by heap_getnext() are pointers onto
     *  disk pages and were not created with palloc() and so should not
     *  be pfree()'d.
     * ----------------
     */
    slot = scanstate->css_ScanTupleSlot;  

    slot = ExecStoreTuple(tuple,  /* tuple to store */
			  slot,   /* slot to store in */
			  buffer, /* buffer associated with this tuple */
			  false); /* don't pfree this pointer */

    /* ----------------
     *  XXX -- mao says:  The sequential scan for heap relations will
     *  automatically unpin the buffer this tuple is on when we cross
     *  a page boundary.  The clearslot code also does this.  We bump
     *  the pin count on the page here, since we actually have two
     *  pointers to it -- one in the scan desc and one in the tuple
     *  table slot.  --mar 20 91
     * ----------------
     */
    ExecIncrSlotBufferRefcnt(slot);

    return slot;
}

/* ----------------------------------------------------------------
 *	ExecSeqScan(node)
 *
 *   	Scans the relation sequentially and returns the next qualifying 
 *   	tuple.
 * 	It calls the ExecScan() routine and passes it the access method
 *   	which retrieve tuples sequentially.
 *   
 */

TupleTableSlot *
ExecSeqScan(SeqScan *node)
{
    TupleTableSlot	*slot;
    Plan  		*outerPlan;

S_printf("ExecSeqScan: scanning node: "); S_nodeDisplay(node);

    /* ----------------
     * if there is an outer subplan, get a tuple from it
     * else, scan the relation
     * ----------------
     */
    outerPlan = outerPlan((Plan *) node);
    if (outerPlan) {
	slot = ExecProcNode(outerPlan, (Plan*) node);
    } else {
	slot = ExecScan(node, SeqNext);
    }

S1_printf("ExecSeqScan: returned tuple slot: %d\n", slot);

    return slot;
}

/* ----------------------------------------------------------------
 *   	InitScanRelation
 *
 *	This does the initialization for scan relations and
 *	subplans of scans.
 * ----------------------------------------------------------------
 */
Oid
InitScanRelation(SeqScan *node, EState *estate,
		 CommonScanState *scanstate, Plan *outerPlan)
{
    Index	        relid;
    List	        *rangeTable;
    RangeTblEntry       *rtentry;
    Oid			reloid;
    TimeQual		timeQual;
    ScanDirection   	direction;
    Relation		currentRelation;
    HeapScanDesc    	currentScanDesc;
    RelationInfo	*resultRelationInfo;

    if (outerPlan == NULL) {
	/* ----------------
	 * if the outer node is nil then we are doing a simple
	 * sequential scan of a relation...
	 *
	 * get the relation object id from the relid'th entry
	 * in the range table, open that relation and initialize
	 * the scan state...
	 * ----------------
	 */
	relid =   		node->scanrelid;
	rangeTable = 		estate->es_range_table;
	rtentry = 		rt_fetch(relid, rangeTable);
	reloid =  		rtentry->relid;
	timeQual = 		rtentry->timeQual;
	direction =  		estate->es_direction;
	resultRelationInfo = 	estate->es_result_relation_info;
	
	ExecOpenScanR(reloid,		  /* relation */
		      0,		  /* nkeys */
		      NULL,	          /* scan key */
		      0,		  /* is index */
		      direction,          /* scan direction */
		      timeQual, 	  /* time qual */
		      &currentRelation,   /* return: rel desc */
		      (Pointer *) &currentScanDesc);  /* return: scan desc */
	
	scanstate->css_currentRelation = currentRelation;
	scanstate->css_currentScanDesc = currentScanDesc;
	
	ExecAssignScanType(scanstate, 
			   RelationGetTupleDescriptor(currentRelation));
    } else {
	/* ----------------
	 *   otherwise we are scanning tuples from the
	 *   outer subplan so we initialize the outer plan
	 *   and nullify 
	 * ----------------
	 */
	ExecInitNode(outerPlan, estate, (Plan*)node);
	
	node->scanrelid = 0;
	scanstate->css_currentRelation = NULL;
	scanstate->css_currentScanDesc = NULL;
	ExecAssignScanType(scanstate, NULL);  
	reloid = InvalidOid;
    }

    /* ----------------
     *	return the relation
     * ----------------
     */
    return reloid;
}


/* ----------------------------------------------------------------
 *   	ExecInitSeqScan
 *
 * old comments
 *   	Creates the run-time state information for the seqscan node 
 *   	and sets the relation id to contain relevant descriptors.
 *   
 *   	If there is a outer subtree (sort), the outer subtree
 *   	is initialized and the relation id is set to the descriptors
 *   	returned by the subtree.
 * ----------------------------------------------------------------
 */
bool
ExecInitSeqScan(SeqScan *node, EState *estate, Plan *parent)
{
    CommonScanState     *scanstate;
    Plan	        *outerPlan;
    Oid			reloid;
    HeapScanDesc	scandesc;

    /* ----------------
     *  assign the node's execution state
     * ----------------
     */
    node->plan.state = estate;

    /* ----------------
     *   create new CommonScanState for node
     * ----------------
     */
    scanstate = makeNode(CommonScanState);
    node->scanstate = scanstate;

    /* ----------------
     *  Miscellanious initialization
     *
     *	     +	assign node's base_id
     *       +	create expression context for node
     * ----------------
     */
    ExecAssignNodeBaseInfo(estate, &scanstate->cstate, parent);
    ExecAssignExprContext(estate, &scanstate->cstate);

#define SEQSCAN_NSLOTS 3
    /* ----------------
     *	tuple table initialization
     * ----------------
     */
    ExecInitResultTupleSlot(estate, &scanstate->cstate);
    ExecInitScanTupleSlot(estate, scanstate); 

    /* ----------------
     *	initialize scan relation or outer subplan
     * ----------------
     */
    outerPlan = outerPlan((Plan *)node);

    reloid = InitScanRelation(node, estate, scanstate, outerPlan);

    scandesc = scanstate->css_currentScanDesc;
    scanstate->cstate.cs_TupFromTlist = false;

    /* ----------------
     * 	initialize tuple type
     * ----------------
     */
    ExecAssignResultTypeFromTL((Plan*)node, &scanstate->cstate);
    ExecAssignProjectionInfo((Plan*)node, &scanstate->cstate);

    return TRUE;
}

int
ExecCountSlotsSeqScan(SeqScan *node)
{
    return ExecCountSlotsNode(outerPlan(node)) +
	ExecCountSlotsNode(innerPlan(node)) +
	    SEQSCAN_NSLOTS;
}

/* ----------------------------------------------------------------
 *   	ExecEndSeqScan
 *   
 *   	frees any storage allocated through C routines.
 *|	...and also closes relations and/or shuts down outer subplan
 *|	-cim 8/14/89
 * ----------------------------------------------------------------
 */
void
ExecEndSeqScan(SeqScan *node)
{
    CommonScanState	*scanstate;
    Plan		*outerPlan;

    /* ----------------
     *	get information from node
     * ----------------
     */
    scanstate = node->scanstate;

    /* ----------------
     *	Free the projection info and the scan attribute info
     *
     *  Note: we don't ExecFreeResultType(scanstate) 
     *        because the rule manager depends on the tupType
     *	      returned by ExecMain().  So for now, this
     *	      is freed at end-transaction time.  -cim 6/2/91     
     * ----------------
     */    
    ExecFreeProjectionInfo(&scanstate->cstate);

    /* ----------------
     * close scan relation
     * ----------------
     */
    ExecCloseR((Plan*) node);

    /* ----------------
     * clean up outer subtree (does nothing if there is no outerPlan)
     * ----------------
     */
    outerPlan = outerPlan((Plan *)node);
    ExecEndNode(outerPlan, (Plan*)node);

    /* ----------------
     *	clean out the tuple table
     * ----------------
     */
    ExecClearTuple(scanstate->cstate.cs_ResultTupleSlot);
    ExecClearTuple(scanstate->css_ScanTupleSlot); 
}

/* ----------------------------------------------------------------
 *   			Join Support
 * ----------------------------------------------------------------
 */
/* ----------------------------------------------------------------
 *   	ExecSeqReScan
 *   
 *   	Rescans the relation.
 * ----------------------------------------------------------------
 */
void
ExecSeqReScan(SeqScan *node, ExprContext *exprCtxt, Plan* parent)
{
    CommonScanState 	  *scanstate;
    EState	  *estate;
    Plan	  *outerPlan;
    Relation      rdesc;
    HeapScanDesc  sdesc;
    ScanDirection direction;

    scanstate = node->scanstate;
    estate =    node->plan.state;

    outerPlan = outerPlan((Plan*)node);
    if (outerPlan) {
      /* we are scanning a subplan */
	outerPlan = outerPlan((Plan *)node);
	ExecReScan(outerPlan, exprCtxt, parent);
      } else {
	/* otherwise, we are scanning a relation */
	rdesc = 	scanstate->css_currentRelation;
	sdesc = 	scanstate->css_currentScanDesc;
	direction = 	estate->es_direction;
	sdesc = 	ExecReScanR(rdesc, sdesc, direction, 0, NULL);
	scanstate->css_currentScanDesc = sdesc;
    }
}

/* ----------------------------------------------------------------
 *   	ExecSeqMarkPos(node)
 *   
 *   	Marks scan position.
 * ----------------------------------------------------------------
 */
void
ExecSeqMarkPos(SeqScan *node)
{
    CommonScanState 	 *scanstate;
    Plan	 *outerPlan;
    HeapScanDesc sdesc;

    scanstate =     node->scanstate;

    /* ----------------
     *	if we are scanning a subplan then propagate
     *  the ExecMarkPos() request to the subplan
     * ----------------
     */
    outerPlan = outerPlan((Plan*)node);
    if (outerPlan) {
	ExecMarkPos(outerPlan);
	return;
    }

    /* ----------------
     *  otherwise we are scanning a relation so mark the
     *  position using the access methods..
     *
     * ----------------
     */
    sdesc = scanstate->css_currentScanDesc;
    heap_markpos(sdesc);

    return;
}

/* ----------------------------------------------------------------
 *   	ExecSeqRestrPos
 *   
 *   	Restores scan position.
 * ----------------------------------------------------------------
 */
void
ExecSeqRestrPos(SeqScan *node)
{
    CommonScanState	 *scanstate;
    Plan	 *outerPlan;
    HeapScanDesc sdesc;

    scanstate = node->scanstate;

    /* ----------------
     *	if we are scanning a subplan then propagate
     *  the ExecRestrPos() request to the subplan
     * ----------------
     */
    outerPlan = outerPlan((Plan*)node);
    if (outerPlan) {
	ExecRestrPos(outerPlan);
	return;
    }

    /* ----------------
     *  otherwise we are scanning a relation so restore the
     *  position using the access methods..
     * ----------------
     */
    sdesc = scanstate->css_currentScanDesc;
    heap_restrpos(sdesc);
}
